Apparatus for grinding



Dec. 28, 1948. F.. G. KRAFFT ,4

APPARATUS FOR GRINDING I Filed Spt. 21, 1946 4 Sheeth l FIG. l

l l H8 74 72 INVENTOR FREDERICH 6. KRAFFT.

4; ATTORNEYS Dgg. 28, 1948. KRAFFT 2,457,383

APPARATUS FOR-GRINDING Filed Sepfip 21,1946

4 Sheets-Sheet 2 INVENTOiQ FREDERICH G. KRAE FT,

ATTORNEYS Dec. 28, 1948. Y F. G. KRAFFT" APPARATUS FOR GRINDING 4 Sheets-Sheet 3 Filed Sept. 21, 1946 BY J 'i ATTORNEYS Dec. 28, 1948. F. G. KRAFFT 2,457,383

APPARATUS FOR GRINDING Filed Sept. 21, 81946 '4 Sheets-She et 4- INVENTOR I '00 I FREDERICH G .K RAFFT,

' I BY 3 I 9|4 LWQW I ATTORNEYS Patented Dec. 28, 1948 UNITED STATES PATENT OFFICE 2,4571'383 APPARATUS FOR GRINDING Frederich G. Kraift, Springfield, Ohio, assignor to The Thompson Grinder Company, Springfield, Ohio, a corporation of Ohio Application September 21, 1946, Serial No. 698,500

9 Claims.

This invention relates to methods and apparatus in connection with grinding machines. More particularly, this invention relates to a method of grinding workpieces and to a novel fixture for supporting the workpieces during the said grinding thereof.

The particular object of the present invention is the provision of an improved process and mechanism for the production of thread rolling dies. Dies of this nature comprise substantially flat plates which have threads formed thereon. In use, a pair of such dies are placed face to face and form threads on a screw onWorkpiece by rolling it therebetween under pressure. '"This is a fast and economical way of forming threads of commercial accuracy. While the thread dies are in some cases flat, it is preferable that they include an inclinedportion over about one-half their length andhave rounded end portions. The rounded end portions facilitate the entry and exit of a workpiece to and from the pair of dies while the inclined portion simulatesa feed so that the threads are gradually rolled into the workpiece.

Heretofore, the production of thread dies of this nature was attended with diiliculty because of the aforementioned rounded and inclined portions of the surface thereof. In order properly to grind a die of this nature it is essential that it be ground from end to end in a single pass of the grinding wheel. This necessitates adjustment of the position of "the wheel and workpiece relative to each other. Formerly it was attempted to move the grinding wheel toward and away from the workpiece'during the grinding operation but it was found that inferior workpieces resulted due to the great inertia of the grinding wheel and its supporting structure. Also, former grinding techniques involved the use of a wheel having a single thread formed thereon so that in the forming of a thread rolling die it was necessary to make several passes across the workpiece and to duplicate the movements of the die and wheel relative to .each other on each pass. I

With the present invention the foregoing difiiculties are eliminated by grinding a thread rolling die ata single pass,- and by moving the said die radially toward and away from the grinding wheel in order to obtain the desired configuration.

Accordingly, the principal object of the present invention is to provide a method and apparatus for grinding workpieces such as thread rolling dies with a single pass of the grinding wheel.

A still further object is the provision of an improved workpiece holding fixture for grinding machines which moves the workpiece relative to the wheel in order to grind predetermined contours thereon.

These and other objects and advantages will become more apparent upon reference to the following description taken in connection with the attached drawings in which:

Figure 1 is a fragmentary View of a grinding machine showing the grinding wheel, the work-- piece "supporting fixture, and a dressing means for dressing the periphery of the wheel;

Figure 2 is a view similar to Figure 1 but partially broken away to show the mechanism for substantially along tion of the dressing mechanism for a grinding wheel;

Figures 7, 8 and 9 are views showing the fixture and workpiece at difierent stages of a grinding cycle.

General arrangement According to this invention it is desired to grind thread forms or the like in a die plate from end to end and to form the said plate with a relieving fillet at each end and with a tapered or inclined portion extending from one end part way to the other. For accomplishing this result, the

workpiece is supported on a fixture having suitablechuck means such as electric or magnetic chuck.

The fixture is'supported for movement toward and the wheel to cut the straight inclined portion indicated at] Ill on the workpiece.

Whenthe'rightward movement of the table has progressed to the point where'the shaft 38 is stopped in its rotation, the wheel is positioned at the beginning of the straight portion H2 of the workpiece. Thereafter, the movement of the table'to the right causes'no tilting of the fixture 24 untilthe roller'92 meets th'e'rise Illa of the cam 94." When this occurs, the shaft 42'is rotated clockwise and the'eccentric portion 44 thereof lifts the left end of the fixture 24 so that the grinding wheel cuts the'fillet or relief portion indicated at I'M on the workpiece. It 'will be apparent that the fixture 24 is guided throughout the grinding cycle by the guiding pads shown at 50, 52 and the collars 54 and 56 and the ball guide 62 together with the brackets 58 and 60.

Following the grinding of the workpiece, if it is desired to true the wheel the table may be moved to bring the grinding wheel 20 directlyiover the dressing roller indicated at I It. Thereafter, the wheel may be dressed by running it together with the said roll under pressure and with no slipping therebetween. This type of dressing is known as crush dressing or crush forming of the wheel and is particularly well adapted for the work cycle illustrated in the present application.

In order to make the arrangement of this invention adaptable for workpieces of different sizes, the bar 14 may carry scale marks as indicated at H8 which register with the marks I20 and I22 carried by the supporting feet of the cams l2 and 94. It will be apparent that the present invention provides a method of, and apparatus for, grinding a workpiece including fillets and inclined surfaces as well as fiat surfaces in a standard grinding machine without in any way altering the said machine except to provide a suitable support for the cam carrying bar i l. Thus, by practicing the methods of this invention and utilizing the apparatus thereof, the field of use of a standard grinding machine is greatly extended and workpieces which have heretofore only been formed with great difficulty, may be ground rapidly, accurately, and economically.

It will be understood that this invention is susceptible to modification in order to adopt it to different usages and conditions and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. In a grinding machine; a rotatable grinding wheel; a workpiece supporting fixture; eccentric means supporting said fixture at each end; an arm on each eccentric means; a cam for each arm; means for relatively reciprocating said wheel and fixture for grinding a workpiece carried on the latter; and means for simultaneously moving said arms and cams relatively for actuating said eccentric means for a predetermined sequence of tilting movements of said fixture.

2. A fixture for supporting a workpiece on a machine table comprising; a base rigidly securable to the table; a workpiece supporting member; guide means for limiting the movements of said member on said base to tilting movements or to movements of the member directly toward and away from said base; eccentric means engaging said member at spaced points; and means operable automatically as the machine table is reciprocated for actuating said eccentric means in rotation for tilting said member to contour a workpiece thereon.

3. In a machine tool; a bed; a table reciprocable onsaid bed; a fixture comprisin a base rigidly secured to the table and a workpiece supporting member carried on the base; guide means preventing'lateral orlongitudinal movements of said member on said base while permitting tilting movements thereof; an eccentric shaft supporting' said member at each end; an arm on each shaft; cam means on said bed to engage and actuate said arms; and means for reciprocating said table on said bed whereby said member goes through a predetermined tilting cycle for each stroke of said table.

4. In a machine tool having a relatively reciprocable cutting means and workpiece supporting table; a fixture comprising a base rigidly securable to said table; a workpiece supporting member on said base; guide means limiting the movement of said member relative to said base to tilting movements in a single plane; spaced eccentric means journalled in said base and directly supporting said member; an arm on each said eccentric means; cam means operable when said arms and cam means move relatively to actuate said eccentric means; and means for synchronously actuating said cutting means and table, and said cam means and arms in relative reciprocating movements.

5. In a fixture for supporting a workpiece to be machined; a base; a pair of spaced eccentric shafts journalled in said base; a workpiece holding member supported on said shafts; yielding means continuously urging said shafts in one di rection; stop means to halt said shafts in the said one direction to predetermine a position of said member; an arm on each shaft; cam means to engage and actuate said arms; and means operable in synchronism with the traversing of said workpiece by a cutting tool for moving said cam means relative to said arms.

6. In a fixture for supporting a workpiece while it is being machined; a base; an eccentric shaft journalled in each end of said base; yielding means continuously urging said shafts into predetermined stopped positions; a workpiece holding member supported on said shafts; guides holding said member against transverse movement on said base; a ball guide extending from said base intermediate said shafts; bracket means on said member embracing said ball guide; and means for oscillating said shafts for tilting said member during the machining o' a workpiece thereon.

'7. In a grinding machine having a bed and table reciprocable thereon; a fixture on said table comprising a base rigid thereon; a work holding member guided on said base for tilting movements; an eccentric shaft at each end of said base supporting said member; an arm on each shaft; cam means for actuating said arms to rotate said shafts for tilting said member; and bracket means on said bed for supporting said cam means in alignment with said arms.

8. In a grinding machine having a bed and table reciprocable thereon; a fixture on said table comprising a base rigid thereon; a work holding member guided on said base for tilting movements; an eccentric shaft at each end of said base sup porting said member; an arm on each shaft; separate cam means for actuating said arms independently to rotate said shafts for tilting said member; and bracket means on said bed for adjustably supporting said cam means in alignment with said arms.

9. In a grinding machine having a bed and table reciprocable thereon; a fixture on said table qeeipr sine a ba e. i d th a w hQ di member guided on said base for tilting movemer ts; an eccentric shaft at each end. of said base supporting said member; an arm on each shaft cam means for actuating said arms to retatesaid shafts for tilting said member; and graduated bracket means on said bed for sepa rately supperting said cam means in alignment with said arms and for independent adjustability.

FREDERICK-1 G. Kar m.

8 REFERENCES CITED The following references are of record in the file of this patent:

5 UNITED STATES PATENTS Number Name Date 1,330,981 Donner Feb. 17, 1920 1,970,000 Dunbar et a1 Au 14, 1934 10 2,082,734 Grlfling et a1 June 1,1937

FOREIGN PATENTS Numbe Co n Date 309,270 Great Britain Apr. 11, 1929 

